The present invention relates generally to the production of bent glass sheets, and, more particularly, to an improved apparatus for bending glass sheets to special configurations that incorporates an S-shaped transverse bend as well as a longitudinal bend. More specifically, this invention relates to special stop members of a particular structure particularly useful with outline molds used to shape glass sheets to such complicated shapes.
Bent glass sheets are commonly used as glazing closures in vehicles such as automobiles and the like. For such applications, the glass sheets must be bent to precisely defined curvatures dictated by the configuration and outline of the vehicle openings in which the sheets are to be installed as well as the overall styling of the vehicle. At the same time, it is important that the bent sheets meet very stringent optical requirements so that the viewing area of the resulting shaped window is free of optical defects that would interfere with good vision through the window. For certain windows used as glazing closures, the bent glass sheets are tempered to strengthen them and increase their resistance to damage resulting from impact. Furthermore, in the less frequent breakage of tempered glass, the resulting particles are relatively small and smoothly surfaced and thus are less likely to cause damage to an occupant of a vehicle than untempered glass, which fractures under less severe loads and causes particles having jagged edges of a larger size that are more likely to injure vehicle occupants.
In recent years, the glass sheets have been press bent into complicated shapes while suspended from tongs. However, tongs tend to penetrate into the major surfaces of the glass and provide localized portions that have poor optical properties as well as providing mechanical weakness for the glass in the vicinity of the points gripped by the tongs.
It has also been customary in the glass sheet bending art to press bend glass sheets supported in a horizontal position, either on a series of conveyor rolls, or by a gaseous hearth bed which supports the glass in close relation thereover by hot gas, lifting the glass sheet on a vertically movable outline mold from proximity to the support plane provided either by conveyor rolls or the gaseous support bed into engagement with a vacuum holder and then depositing the glass onto a ring-like member which is interposed between the plane of support and the bottom surface of the vacuum holder. Prior to the present invention, most of the shapes produced by such apparatus were either simple bends or compound bends comprising fairly simple curvatures in both mutually perpendicular directions. The need for a glass sheet alignment member becomes greater when the glass sheet is to be shaped to a more complicated shape defined by a downwardly facing surface of a vacuum mold and by an upwardly facing surface of complementary shape of the vertically movable outline lifting mold. Furthermore, when the glass sheet is shaped by moving the sheet while heat-softened over a gaseous hearth bed having a downwardly curved downstream end portion that curves downward to cause the glass sheet to flow downward and sag along its leading edge portion, it is important to have alignment means in position to engage the leading edge of the glass sheet even when the vertically movable outline mold occupies a recessed position. It is equally important that once the glass sheet is properly aligned, it remains aligned until it is engaged by vacuum against the downwardly facing shaping surface of the upper vacuum mold.
U.S Pat. No. 2,570,309 to Black discloses apparatus for bending a single glass sheet by a combination of gravity sagging a heated glass sheet on an outline mold and then lifting the sagged glass sheet while still hot off the outline mold onto a solid lower pressing mold that engages the hot glass sheet against an upper pressing mold of complementary shape to complete its shaping by press bending and then returning the press bent glass sheet to the outline mold. No edge alignment means is depicted in this patent to insure that the glass sheet is properly aligned with the outline mold and between the pressing molds.
U.S. Pat. No. 2,695,476 to Jendrisak and U.S. Pat. No. 2,729,032 to White disclose outline molds that have glass edge engaging members that pivot inward to follow the edges of the glass sheet as it sags toward the outline mold. The glass edge engaging members must be removed manually to remove the bent glass sheet from the mold. Other patents showing this feature includes U.S. Pat. Nos. 2,744,359; 2,758,422; 2,774,189; 2,798,338 and 2,859,561, all to Jendrisak.
U.S. Pat. No. 2,814,164 and U.S. Pat. No. 3,089,319 to Carson and White disclose outline molds having universally pivotable stops that follow and engage pointed tips at the opposite longitudinal edges of glass sheets supported for bending on the outline mold to control tip overbending as well as positioning.
U.S. Pat. No. 2,840,953 to Black and U.S. Pat. No. 3,023,542 to Babcock disclose bimetal actuators attached to glass edge guide members to change the location of the guide members in response to a change in temperature during the bending cycle. When the mold is cool, the bimetal actuators position the edge guides into proper positions for aligning a glass sheet edge. When the mold is heated to heat soften the glass, the bimetal actuators move the edge guide members out of contact with the glass, thus losing the contact between the guide members and the glass sheet edge that maintains the glass in proper mold alignment.
U.S. Pat. No. 2,901,866 and U.S. Pat. No. 3,162,523 to McKelvey and U.S. Pat. No. 3,103,430 to Jendrisak disclose outline molds with counterweighted, pivoted glass engaging members that pivot against the glass sheet edge as the glass sags toward the shaping surface of the outline mold. No provision is made to disengage the glass edge after the glass bend is completed except for manual operation.
U.S. Pat. No. 3,060,708 to Stickel discloses a sectionalized mold having glass edge engaging members mounted to move away from the glass edge as the mold sections close to provide a substantially continuous outline shaping surface. The alignment is lost as soon as the engagement members disengage from the glass edge.
U.S. Pat. No. 3,220,822 to Jendrisak discloses sectionalized outline molds having a pivoted end portion for each end mold section that follow the ends of the glass sheet as the latter shortens from a flat shape to a shape curved in elevation. Manual operation is also required here to separate the end portions from the bent glass sheet.
U.S. Pat. No. 3,230,067 to Carson and Stickel discloses an outline sectionalized shaping mold comprising pivotally supported shaped members that serve both as edge guides and supports for the flat glass sheet that rotate outwardly from the guided side edges as the mold closes and the glass sheet sags. Outward rotation permits the likelihood of glass sheet misalignment during shaping.
U S. Pat. No. 3,846,104 to Seymour illustrates a number of Patents that shape glass sheets to a non-uniform shape by delivering one or more heat-softened glass sheets at a time into a position at a shaping station over a gaseous hearth bed having an upwardly facing surface beneath an upper vacuum mold. A lower outline pressing mold of complementary shape is located in vertical alignment below the upper vacuum mold and moves between a retracted position below the upper surface of the bed and an upper position near the upper vacuum mold. The lower outline pressing mold rises to engage the glass sheet(s) against the upper vacuum mold to cause the heat-softened glass sheet to develop a shape conforming to that of the vacuum mold. Suction applied to the upper vacuum mold holds the shaped glass sheet against its lower shaping surface while the lower outline pressing mold retracts to enable a ring-like member having an outline shaping surface that conforms to the supported portion of the glass sheet adjacent its perimeter to shuttle into position below the vacuum mold. The vacuum on the vacuum mold is ended and the shaped glass sheet falls onto the ring-like member which supports the shaped glass sheet adjacent its perimeter for transfer to a cooling station where the glass is cooled sufficiently rapidly to develop a desired degree of temper. To the best of our knowledge, no apparatus of this type has been developed to shape glass sheets to a compound bend comprising a transverse bend component of S-shaped configuration and a longitudinal bend component of concave elevation.
U.S. Pat. No. 4,217,126 to Hagedorn et al. discloses press bending apparatus for bending glass sheets to compound curvatures including a reversely curved portion that is bent in a direction opposite the direction at which a glass sheet sags. The apparatus of this patent comprises a tunnel heating furnace, a shaping station having an upper shaping mold, a discontinuous ring-like lower shaping mold having a downwardly curved transversely extending shaping rail adjacent the furnace, shaping pads within the outline of the ring-like lower shaping mold, a pair of piston-actuated stops, and a series of spaced, special conveyor rolls that support a heat-softened glass sheet for movement into the shaping station where the lower shaping mold and shaping pads lift the glass sheet into engagement with the upper shaping mold and then retract to enable the special conveyor rolls to convey the bent glass to a cooling station. The lack of a continuous edge support for the shaped glass results in edge wrinkles. Also, the location of the downwardly curved transversely extending shaping rail adjacent the furnace complicates the shaping operation because this patent tries to impart a transverse bend to the trailing end portion of a glass sheet and the temperature gradient established along the glass sheet length comprises a more readily shapable hotter leading end portion and a less hot trailing end portion that is less likely to sag than the hotter leading end portion. Furthermore, since this patent uses stops actuated by pistons, the latter must be operated precisely in timed sequence to the other steps of a bending operation and, therefore, may require maintenance.
U.S. Pat. No. 4,272,275 to Reese discloses apparatus for press bending glass sheets that are sag bent to an outline shape of an outline mold and are conveyed into a compound bending station having upper and lower press bending molds of complicated shape including a transverse bend of S-shaped configuration. There, the lower press bending mold lifts the preliminarily bent glass sheet into engagement with the upper press bending mold to develop a compound glass sheet shape. The lower press bending mold lowers to redeposit the compound bent glass onto the outline mold. The apparatus of this patent includes glass edge engaging members for the outline mold that occupy a glass engaging position during one phase of a shaping cycle (such as when the glass is initially conveyed on the outline mold to develop a longitudinal component of bend) and are suddenly and automatically removed from glass edge engagement immediately before the longitudinally bent glass is lifted from the outline mold for further processing. Such glass edge engaging members cannot continue to align the glass sheet on the outline mold when returned thereto after further processing. In addition, the glass edge engagement members must be reset in proper position by hand for a subsequent cycle.
It would be beneficial for the glass sheet shaping art to develop apparatus for bending glass sheets to a compound bend including a transverse bend component of S-shaped configuration and a longitudinal bend component that includes glass edge alignment members that establish a position of alignment for a glass sheet arriving at a shaping station and that maintains the alignment with the complicated shape of a vacuum mold by incorporating glass edge alignment members that remain in glass locating position from the time the glass sheet arrives over an outline lifting mold and remains in place throughout its lifting into engagement with the upper vacuum mold without causing damage to the glass edge or any shaping station parts.